After reviewing his past debates, the NY Times asks:

I would say that in this stage of the campaign, still leading in polls, Giuliani will play nice with his rivals. One thing that will be interesting to watch is whether the lower-tier candidates will spend more time attacking Giuliani or Romney. While Giuliani is the current front-runner, Romney is occupying space as a conservative alternative, so Gilmore, Huckabee, Brownback, etc. all have to get past him before challenging Giuliani. Most likely, what we’ll see is the lower tier candidates attacking the top three as a group, arguing that none of them are real conservatives who deserve to lead the party of Reagan.

Given that the debate is this early, it’s unlikely to have much of an impact. For the top tier, the main goal should be to avoid major mistakes that could be used against them down the road. Meanwhile, if one of the bottom tier candidates has a strong showing, it would give him a boost. But if none of the candidates impresses, Fred Thompson will come away as the big winner. He has achieved mythical status to those conservatives unsatisfied with the current crop of candidates, and a lackluster debate will just add to that.